A mold clamping apparatus used for a molding machine such as an injection molding machine or a die casting machine includes a stationary die plate that holds one of a pair of molds (stationary mold), and a movable die plate that holds the other (movable mold), and applies a force between the stationary die plate and the movable die plate in mold clamping to perform mold clamping of the pair of molds. A mold clamping force required for the mold clamping is applied by, for example, generating tension in a plurality of tie bars provided between the stationary die plate and the movable die plate.
Generally, the plurality of tie bars are placed symmetrically with respect to the center of the stationary die plate and the movable die plate so as to provide uniform distribution of the mold clamping force applied to the split surface of the mold, and each tie bar bears the same amount of load (tie bar load).
When the center of gravity of a molded product is offset from the center of the mold clamping apparatus, a force to open the mold (a force to separate the stationary mold from the movable mold) generated by pressure of a molding material applied in a cavity formed by the stationary mold and the movable mold acts on a position offset from the center of the mold clamping apparatus. Thus, if a uniform mold clamping force is applied when the center of gravity of the molded product is offset from the center of the mold clamping apparatus, a force applied to a split surface between the stationary mold and the movable mold on the side with the center of gravity of the molded product being offset becomes non-uniform, thereby creating a gap in the split surface and easily producing burrs.
To solve a problem that the molding material spouts from the split surface in a molding cycle, it is contemplated that loads on the plurality of tie bars are uniformly increased to increase the mold clamping force, but this method may apply an excessive load to the mold to reduce the life of the mold.
A mold clamping apparatus that can prevent a molding material from spouting from a split surface of a mold, and can extend the life of the mold is disclosed in Patent Document 1. The mold clamping apparatus includes a control device that determines a mold clamping force borne by each of a plurality of tie bars based on information on the mold, and independently controls oil pressure in a cylinder chamber of each mold clamping cylinder so as to obtain the determined mold clamping force.    Patent Document 1: Japanese Patent Laid-Open No. 2005-324249